Reactive oxygen species requirements for bovine sperm capacitation and acrosome reaction

Abstract

Sperm capacitation is necessary for the fertilization of oocytes. During capacitation intracellular and membrane changes occur, that culminate with an exocytotic event called the acrosome reaction. The aim of this work was to study the participation of the Superoxide anion (O 2 ∸) and of hydrogen peroxide (H 2O 2) in the capacitation process and acrosome reaction in spermatozoa from cryopreserved bovine semen. Samples were capacitated with heparin or treated with the xanthine-xanthine oxidase-catalase system (X-XO-C) for the production of O 2 ∸. The percentage of capacitated spermatozoa was determined using the chlortetracycline (CTC) technique, by means of epifluorescence microscopy. Addition of X-XO-C to the incubation medium significantly induced capacitation (P<0.05), but there were no differences with samples incubated with heparin. When the medium contained heparin or the X-XO-C, addition of Superoxide dismutase (SOD, 0.5 mg/mL) significantly inhibited capacitation (P<0.05). In samples treated with heparin and with diverse concentrations of H 2O 2 (10, 25, 50 and 250 μM) in the incubation medium, the percentage of capacitated spermatozoa was significantly reduced (P<0.05); however, acrosome reaction was produced at concentrations of 10 and 25 μM H 2O 2. At concentrations greater than 25 μM H 2O 2 a deleterious effect was observed on sperm motility. From these results it may be inferred that O 2 ∸ is required in the capacitation process and that H 2O 2 may participate as an inductor of the acrosome reaction in spermatozoa from cryopreserved bovine semen.